Scientists predict how to detect a new dimension

Cynric said:
One of the scientists said something along the lines of "these extra dimensions may be as small as a few millimetres across". WTF? How can you describe a width for a dimension? It's not as if you can say that "height" is about four feet wide.
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Here's what I think they meant:

Let's say we have one of these small dimensions along the w-axis: If you travel more than a few millimeters along the w-axis, you'll find yourself looping around the same point.
 
BronzeDog said:
Here's what I think they meant:

Let's say we have one of these small dimensions along the w-axis: If you travel more than a few millimeters along the w-axis, you'll find yourself looping around the same point.
Click to expand...

Must be an echo in here :)

GMTA, eh? Although millimeters would be easily detectable, IIRC current theories posit very, very tiny scales (possibly micrometers, but more likely nanometers. Can't remember currently).
 
Anyway, be sure to stop by the TTL: Posted a list topic where people can helpfully tell me about what I've missed.
 
athon said:
Jimbo, this is why I still come back to this board.
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Wow! That's far too kind, especially considering that epepke's next post laid bare all of the physics I haven't been exposed to, much less understand...

BronzeDog said:
Let's say we have one of these small dimensions along the w-axis: If you travel more than a few millimeters along the w-axis, you'll find yourself looping around the same point.
Click to expand...

I've gone back and reread the NOVA article and the OP article. The OP doesn't invoke string theory. It talks about a 5-dimensional theory of gravity. The OP article clearly states that it is talking about 4 spatial dimensions and time.

Is this last dimension 'curled up'? Is that the only possible geometry for a 4th spatial dimension? If so, then BD would be correct, right? Travelling along the 4th spatial dimension would involve travelling around a point defined in the other 3. Also, would it be added on to the spatial dimensions required in string theory?

You would need something more than my simple unit vectors. You'd need a mapping for each element as well, to somehow describe the geometry described by the unit vectors. You'd have to use, I don't know, something like the del operator and describe some sort of curl... I'm sure this is what has happened, with all sorts of fun stuff like tensors and tensor fields get thrown in...

It's the nature of my program that most of our 'physics' ends after 3rd year (largely to cover semiconductor physics), so I'm likely to leave my undergrad with a very poor knowledge of GR. So, ep...

epepke said:
I have a guess that the number of dimensions in the universe, including wrapped-up ones, will turn out to map onto one of the hypercomplex numbers, and there are only a limited number of those...
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What is a hypercomplex number? Is it some form of higher-order complex number (instead of 3+i4, you'd have 3+i4+j2...)? If i is a vector rotation, would j be another in another dimension? Or am I on the wrong track and it's something like a matrix rotation (which of course, itself, would exist in a vector space)? Is it something else altogether? Or am I simply not yet capable/ready to bother?
 
Jimbo:

Can't answer all of your questions, but maybe I can shed light on a few.

The reason for the extra dimensions in string theory are because the various properties of particles are defined as vibrations in these higher dimensions. Mass, for example, might be produce by the vibrations of the string in the 8th spatial dimenions (probably not accurate, but gives the idea).

So, when they talk about a 5-dimensional theory of gravity, they're talking about being able to describe the force of gravity as operating at least partly in one of these extra dimenions. They aren't necessarily saying there are only 4 dimensions, orr that there are specifically 5, but that their theory works if you describe gravity with 5 dimensions.

Any extra dimensions would have to be curled up, or we'd notice them. basically, if they were large we'd see the movement in that dimension.

Some theories posit that these curled dimensions provided the impetus for the dimensions we experience to expand (they get smaller, the ones we experience get larger). And, of course, this gets into Callabi-Yau (sp?) spaces and all sorts of higher mathematics that really, really scare me.

Of course, all of the extra-dimensional stuff goes beyond GR. This is where you get into various string theorys, 11d supergravity, E8x8 symmetry, and other proposed theories of everything.
 
Ok, can somebody explain why black holes don't evaporate in this theory?

I keep wondering what would prevent quantum evaporation, and how it would affect other things.

Does this have any predictions for the Higgs Boson, for instance?
 
Psi Baba said:
Having just watched the DVD of The Elegant Universe, and being halfway through the book, I'd say that's a pretty good summary answer to Cynric's question.
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Yes, it was the Elegant Universe (at least, I recognize the presenter).
Thank you all for your heroic efforts at teaching.

The thing I'm struggling with is how additional dimensions can exist "within" the four we can perceive. As others have said, the definition of a dimension is that it cannot be referred to as dependent on any of the others. Therefore, I can see why an object, for example, can be defined within 12 dimensions (simply 12 variables in the vector), but how can one of those 12 dimensions occupy a mm of dimension 3. The whole concept of dimensions having limits baffles me. Unless the existing dimensions are accepted as limited within a spherical volume, meaning height, width, depth (and time) all curve round to meet themselves ultimately.

You see. I am rather confused.
 
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BronzeDog said:
Here's what I think they meant:

Let's say we have one of these small dimensions along the w-axis: If you travel more than a few millimeters along the w-axis, you'll find yourself looping around the same point.
Click to expand...

Ah! Light gutters into life in the distance.
So dimension w doesn't occupy 1 mm (or microm) in dimension x at all. It just occupies 1 mm in dimension w, and so contributes little to a vector defining a point in 12 (or whatever) dimensional space.

Thank you. Very much. :)

[I don't think the big wobbly ribbony thing was a very helpful graphic]
 
Huntsman said:
Must be an echo in here :)

GMTA, eh? Although millimeters would be easily detectable, IIRC current theories posit very, very tiny scales (possibly micrometers, but more likely nanometers. Can't remember currently).
Click to expand...

It's a good thing, Huntsman.
Sometimes I need to hear things twice. ;)
 
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